In a major signal of public support, 150 House Democrats signed a letter Thursday supporting President Barack Obama's framework for a nuclear deal with Iran.

"As negotiations over Iran's nuclear program continue, we urge you to stay on course, building on the recently announced political framework and continuing to work toward a strong and verifiable agreement between the P5+1 countries and Iran that will prevent Iran from having a nuclear weapon," the letter begins. The 150 Democrats — 145 of whom can vote — is a significant number. As the Washington Post points out , if Congress voted to reject the Iranian nuclear deal, and Obama vetoed the rejection, there would appear to be just enough Democrats to sustain the president's veto.

The Senate advanced language Thursday , 98-1, that would give Congress a say over the deal. But the current language would effectively require a two-thirds majority, meaning the 150 Democrats signed onto Thursday's letter — which was written by Jan Schakowsky of Illinois, Lloyd Doggett of Texas and David E. Price of North Carolina — could essentially render input from the rest of Congress meaningless.

Of course, that assumes all Democrats on the letter remain supportive of a deal that would hypothetically be voted down by the rest of Congress. Notably, there are more than 40 Democrats who did not sign the letter, including Minority Whip Steny H. Hoyer of Maryland. Minority Leader Nancy Pelosi of California did sign.

Either way, the Obama administration continues to work out the fine details with Iran and the other permanent countries on the U.N. Security Council (plus Germany, hence the "P5+1" moniker). The outline of the deal would trade a lifting of sanctions on Iran in exchange for a number of concessions on the country's nuclear programs, including U.N. inspections, the scaling back of uranium production and the degradation of Iran's most refined nuclear materials.

But the deal has yet to be finalized. An agreement is set for June 30, but even that deadline could be extended.